共查询到20条相似文献,搜索用时 15 毫秒
1.
Hiroshige Kikura Junichiro Matsushita Yuji Kobayashi Aritomi Masanori 《Science and Technology of Advanced Materials》2013,14(5-6):703-707
This paper reports the experimental research on thermal behaviour and particle size evaluation of primary clusters of ferromagnetic nano-particles in a water-based magnetic fluid. The magnetic fluids are suspensions of ultra fine particles coated with a molecular layer of dispersant in a liquid carrier such as water or kerosene. The particles are coated with single- or double-layer of surfactant to achieve stable dispersion. Numerous experimental studies have indicated the existence of the primary cluster of ferromagnetic nano-particles in a water-based magnetic fluid. The purpose of this research is to evaluate the particle size of the primary clusters by applying the Einstein’s equation for Brownian motion assuming that the primary cluster has a spherical-shape. The thermal behaviour of ferromagnetic nano-particles in magnetic fluids is investigated through the micro visualization using the optical darkfield microscope system and particle tracking velocimetry data processing system. Real-time visualization of the Brownian motion of primary clusters in a water-based magnetic fluid was carried out. The experimental results clarified that the primary cluster size depends upon the concentration of the ferromagnetic nano-particle in the magnetic fluid. 相似文献
2.
Mitsuo Matsuzaki Hiroshige Kikura Junichiro Matsushita Masanori Aritomi Hiroshi Akatsuka 《Science and Technology of Advanced Materials》2004,5(5-6):667
Cluster movements of ferro- and non-magnetic particles in magnetic fluids were investigated using optical microscope system and image processing system. Real-time visualizations of the Brownian motion of particles and the chain-like cluster movement of both types of particle were performed under a magnetic field. The principal objectives of this study were to clarify the applicability of the optical microscope system and image processing system, and to analyze the growth process of the cluster under magnetic field. The analysis of particle image was done using Particle Tracking Velocimetry (PTV). The results clarified that the real-time observation of Brownian motion and cluster movement of ferro- and non-magnetic particles in magnetic fluids can be carried out using the optical microscope system and the PTV image measurement. Independent continuous measurements with changing positions and velocity of the minute particle were made possible. The study concluded that the system can obtain satisfactory results on growth process measurement of cluster under a magnetic field. 相似文献
3.
Mitsuo Matsuzaki Hiroshige Kikura Junichiro Matsushita Masanori Aritomi Hiroshi Akatsuka 《Science and Technology of Advanced Materials》2013,14(5-6):667-671
Cluster movements of ferro- and non-magnetic particles in magnetic fluids were investigated using optical microscope system and image processing system. Real-time visualizations of the Brownian motion of particles and the chain-like cluster movement of both types of particle were performed under a magnetic field. The principal objectives of this study were to clarify the applicability of the optical microscope system and image processing system, and to analyze the growth process of the cluster under magnetic field. The analysis of particle image was done using Particle Tracking Velocimetry (PTV). The results clarified that the real-time observation of Brownian motion and cluster movement of ferro- and non-magnetic particles in magnetic fluids can be carried out using the optical microscope system and the PTV image measurement. Independent continuous measurements with changing positions and velocity of the minute particle were made possible. The study concluded that the system can obtain satisfactory results on growth process measurement of cluster under a magnetic field. 相似文献
4.
In this investigation, nanofluids of carbon nanotubes are prepared and the thermal conductivity and volumetric heat capacity of these fluids are measured using a thin layer technique as a function of time of ultrasonication, temperature, and volume fraction. It has been observed that after using the ultrasonic disrupter, the size of agglomerated particles and number of primary particles in a particle cluster was significantly decreased and that the thermal conductivity increased with elapsed ultrasonication time. The clustering of carbon nanotubes was also confirmed microscopically. The strong dependence of the effective thermal conductivity on temperature and volume fraction of nanofluids was attributed to Brownian motion and the interparticle potential, which influences the particle motion. The effect of temperature will become much more evident with an increase in the volume fraction and the agglomeration of the nanoparticles, as observed experimentally. The data obtained from this work have been compared with those of other studies and also with mathematical models at present proven for suspensions. Using a 2.5% volumetric concentration of carbon nanotubes resulted in a 20% increase in the thermal conductivity of the base fluid (ethylene glycol).The volumetric heat capacity also showed a pronounced increase with respect to that of the pure base fluid. 相似文献
5.
Mynam M Sunthar P Ansumali S 《Philosophical transactions. Series A, Mathematical, physical, and engineering sciences》2011,369(1944):2237-2245
A lattice Boltzmann (LB)-based hybrid method is developed to simulate suspensions of Brownian particles. The method uses conventional LB discretization (without fluid- level fluctuations) for suspending fluid, and treats Brownian particles as point masses with a stochastic thermal noise. LB equations are used to compute the velocity perturbations induced by the particle motion. It is shown that this method correctly reproduces the short-time and long-time diffusive behaviour of a Brownian particle. Unlike the earlier hybrid methods that use thermal fluctuations in the fluid, this method correctly reproduces the temperature of the particle and does not require an empirical rescaling of the bare friction coefficient to obtain the correct diffusive behaviour. It is observed that the present method is at least twice as fast as the earlier method. This method is best suited for flows of polymers and Brownian suspensions in microfluidic devices. 相似文献
6.
David R. Kelland 《Particulate Science and Technology》1985,3(3):101-113
The control, collection or separation of particles on the basis of Their magnetic moment relative Co the carrier fluid has been demonstrated in many applications. Usually the particle sizes are larger than one micron and the magnetic susceptibility at least moderately paramagnetic. Recently, particle separation techniques have been developed for both diamagnetic and submicron particles. These techniques have found application in mineral beneficiation, nuclear reactor coolants, biology and medicine. Such developments require an understanding of flow forces in liquids and gases, diffusion and Brownian motion, and of magnetic properties which range from the strong magnetic moments of ferromagnetic and superparamagnetic particles down orders of magnitude to those of diamagnetism. 相似文献
7.
In this paper, the motion of a chainlike cluster of feeble magnetic particles induced by high magnetic field is discussed on the basis of the results of numerical simulations. The simulations were performed on glass particles with a diameter of 0.8 mm; and the viscosity, applied magnetic field and magnetic properties of the surrounding medium were changed. In addition to the magnetic field and the difference in magnetic susceptibility between the particles and the surrounding medium, the obtained results indicate that the viscosity is an essential factor for the formation of the chainlike alignment of feeble magnetic particles. We also carried out simulations using glass particles with a smaller diameter of 0.1 mm. Chainlike clusters were produced similar to those of ferromagnetic particles formed in a ferromagnetic fluid. 相似文献
8.
DAVID R. KELLAND 《Particulate Science and Technology》2013,31(3-4):101-113
ABSTRACT The control, collection or separation of particles on the basis of Their magnetic moment relative Co the carrier fluid has been demonstrated in many applications. Usually the particle sizes are larger than one micron and the magnetic susceptibility at least moderately paramagnetic. Recently, particle separation techniques have been developed for both diamagnetic and submicron particles. These techniques have found application in mineral beneficiation, nuclear reactor coolants, biology and medicine. Such developments require an understanding of flow forces in liquids and gases, diffusion and Brownian motion, and of magnetic properties which range from the strong magnetic moments of ferromagnetic and superparamagnetic particles down orders of magnitude to those of diamagnetism. 相似文献
9.
AbstractIn this paper, the motion of a chainlike cluster of feeble magnetic particles induced by high magnetic field is discussed on the basis of the results of numerical simulations. The simulations were performed on glass particles with a diameter of 0.8 mm; and the viscosity, applied magnetic field and magnetic properties of the surrounding medium were changed. In addition to the magnetic field and the difference in magnetic susceptibility between the particles and the surrounding medium, the obtained results indicate that the viscosity is an essential factor for the formation of the chainlike alignment of feeble magnetic particles. We also carried out simulations using glass particles with a smaller diameter of 0.1 mm. Chainlike clusters were produced similar to those of ferromagnetic particles formed in a ferromagnetic fluid. 相似文献
10.
We have investigated and modeled the effect of interaction among magnetic particles and the magnitude and duration of external applied magnetic field on Brownian relaxation in a colloidal suspension. In the case of interacting magnetic particles, Brownian relaxation depends on the interparticle dipole-dipole interaction, which slows down the overall Brownian relaxation process of magnetic particles in the colloidal suspension. The individual magnetic particle experiences torque when a pulsatile magnetic field is applied. The torque due to the external field randomizes the particle rotation similar to that of the thermal energy. A faster Brownian relaxation is observed when individual magnetic particles are magnetized for a short duration. Magnetizing the magnetic particle for a longer duration suppress the rotational motion hence the effect of torque on Brownian relaxation. 相似文献
11.
选用无规则、正八面体和六方片状形貌的纳米Fe3O4磁性颗粒制备的磁流体,通过设计、组装磁流体传动性能测试仪,探讨了磁流体传动性能与传动盘间距、传动盘之间的转速差的关系,并研究了磁流体中纳米磁性颗粒的形貌对磁流体传动性能的影响。结果表明,在传动盘间隙一定时,磁流体传递扭矩的大小在磁性粒子未达到其饱和磁化强度时,传递扭矩大小随感应磁场强度增大而迅速增大,但随着磁感应强度的进一步加大,磁性粒子逐步达到其饱和磁化强度,磁流体传递扭矩大小的增长减缓,最后几乎不再增大;传动盘之间的间隙对磁流体传递扭矩的大小影响很大,间隙越大,传递的扭矩越小;传动盘之间的转速差对磁流体传递扭矩的大小影响较小,在低转速差下传递的扭矩随转速差的增加而有所增加,但超过一定的转速差后,由于磁流体的剪切稀化效应,传递的扭矩将有所减小。另外,磁流体中磁性粒子的形貌对磁流体传递扭矩的大小有一定的影响,正八面体形貌的磁性粒子相对于无规则和六方片状形貌的磁性粒子,其磁流体能够传递更大的扭矩。 相似文献
12.
B. É. Kashevskii 《Journal of Engineering Physics and Thermophysics》1999,72(4):722-728
Behavior of a system of single-domain ferromagnetic particles with easy-magnetization-axis-type magnetic anisotropy in a rotating
fluid matrix is considered in a transverse magnetic field that is weak compared to the effective magnetic anisotropy field
of a particle. The dynamics of a separate particle and orientational state of the system are considered with regard for Brownian
rotational diffusion. It is found that a small deviation from the conventional rigid dipole model leads, at frequencies exceeding
a certain critical value, to appearance of two attracting stationary states of the easiest magnetization axis that are situated
in the plane perpendicular to the field and approach, with the growth of a particle, one or another direction of the matrix
rotation axis. It is shown that this circumstance can radically change the behavior of a system of Brownian particles and,
thus, magnetic and hydrodynamic properties of the ferrosuspension. 相似文献
13.
采用化学共沉法制备磁粒子Fe_3O_4,选用表面活性剂油酸进行一次包覆,乳化剂OP(烷基酚聚氧乙烯醚)进行二次包覆制备出稳定的水基磁性液体。利用XRD和TEM分析了样品的结构、形貌及粒径;运用VSM技术研究了样品磁性能;重点考察了油酸和OP用量对水基磁性液体稳定性的影响。结果表明,所制备的Fe_3O_4粒子为球形,颗粒的粒径较均匀细小,在10nm左右;磁性液体显示超顺磁性,饱和磁化强度M_s=54.636A·m~2/kg;油酸和OP用量对磁性液体的稳定性有重要影响,当n(Fe_O_4):n(油酸):n(OP)=5:2:4时,磁性液体的稳定性能最好。 相似文献
14.
15.
A. Józefczak T. Hornowski A. Skumiel V. Závišová M. Koneracká N. Tomašovičová M. Timko P. Kopčanský H. N. Kelani 《International Journal of Thermophysics》2012,33(4):640-652
The effect of the molecular weight of poly(ethylene glycol) (PEG) on the physical properties of water-based magnetic fluids
with sodium oleate and PEG stabilization was investigated. The structure as well as magnetic, rheological, and thermal properties
of the obtained samples were studied using transmission electron microscopy (TEM), photon cross correlation spectroscopy (PCCS),
superconducting quantum interference device (SQUID), and differential scanning calorimetry (DSC) methods. The molecular weight
of PEG had a strong effect on the rheological properties while the effect was rather insignificant on the particle size distribution
and the self-heating of the studied magnetic fluids. The heating ability of the PEG-stabilized magnetic fluids was determined
by calorimetric measurements of the specific absorption rate (SAR). The thickness of the PEG layer was calculated from the
experimental data of the temperature rise rates as a function of the magnetic field strength using the Rosensweig theory. 相似文献
16.
Fouad El-Diasty H.M. El-Sayed F.I. El-Hosiny M.I.M. Ismail 《Current Opinion in Solid State & Materials Science》2009,13(1-2):28-34
An aqueous stable magnetic fluid containing Fe3O4 nano-particles with a mean diameter of 4–7 nm, which is in the range of super-paramagnetism, is prepared. The particles are synthesized via co-precipitation method from ferrous and ferric solutions. X-ray diffraction, transmission electron microscopy, transformer method are used to study the physical properties of the magnetic fluids and powders. A method is given to analyze and resolve the real and imaginary parts of the measured complex susceptibility of magnetic fluids. The band gap parameters of the magneto-nanopowders such as the direct-, indirect-band gap energies, Fermi energy and Urbach energy are determined. A comparative study between the different techniques used to calculate the powder particle size is presented. Adsorption of nitrogen gas is used to identify and determine the particles mean diameter and to study their microstructure, the magnetic properties and surface porosity. The study showed that the total pore system of the magnetic nano-powders consists mainly of mesopores. 相似文献
17.
The paper is devoted to the problem of the determination of regular forces acting on microscopic and smaller objects in fluids when the presence of thermal noise affects the results of measurements. One of the methods on how these forces are determined is the measurement of the drift velocity of Brownian particles. Traditionally such experiments are interpreted on the basis of the overdamped Langevin equation. An exact expression has been obtained for this velocity within the linear hydrodynamic theory of the Brownian motion in incompressible fluids, when the external force is constant and when the particle is in a harmonic potential well. It is shown that for sufficiently short experimental times the influence of the hydrodynamic memory effects in the drift velocity determination is significant. The obtained solutions contain algebraic long-time tails due to which the results expected from the standard theory are approached very slowly with the increase of time. 相似文献
18.
纳米流体热物性的研究作为一门新兴交叉学科一直受到关注,然而至今仍没有理论能够准确解释AuH2O这类体积分数极低的纳米流体导热系数极大增强的现象。因此,在前人理论的基础上,提出一种新的算法模型:利用分形理论模拟纳米颗粒分布来解释团聚物对纳米流体导热系数的影响;利用微对流模型以及颗粒扩散修正因子来还原导热系数的动态项。该算法模型充分考虑了团聚、颗粒分布、布朗运动形成的微对流、温度对颗粒和基液分子布朗运动的影响以及颗粒扩散等因素对纳米流体导热系数的影响,能够准确预测出Au-H2O纳米流体导热系数增强的趋势,理论预测值与绝大部分现有实验数据最大偏差不超过1.5%。研究发现,对这类极低浓度纳米流体而言,温度对其影响大于体积分数和粒径的影响,且呈指数形式增长。 相似文献
19.
Conventional heat transfer fluids have intrinsically poor heat transfer properties compared to solids. Enhancing the efficiency of heat transfer is of great interest for various industrial applications. Suspending solid particles in a fluid increases the thermal conductivity of the resulting suspension and enhances the heat transfer properties. In this work, changes in thermal conductivities of fluids upon the addition of magnetic nanoparticles have been investigated. Fe(3)O(4) nanoparticles are synthesized using different synthesis methods and are suspended in various oils. The effect of the base fluid and the type of magnetic particle on the thermal conductivity is investigated in detail. Up to 28% increase in the thermal conductivity is obtained with 2.5 wt% magnetic particles in hexane. The thermal conductivity enhancement is found to depend on the particle concentration, method of preparation and base fluid. The enhancements obtained are higher than those estimated using any theoretical model present in the literature. 相似文献